Chapter 2: Spanning Tree

Question 1

List the 802.1D port states

Answer 1

Disabled
Blocking
Listening
Learning
Forwarding
Broken

Question 2

Identify the CST port state:

-The port is shutdown.

Answer 2

Disabled

Question 3

Identify the CST port state:

• Port is enabled but not forwarding traffic.
• Can only receive BPDU from other switches.

Answer 3

Blocking

Question 4

Identify the CST port state:

• Port has transitioned from a blocking state and can now send or receive BPDUs.
• Port is capable of becoming root port.
• 15 seconds.

Answer 4

Listening

Question 5

Identify the CST port state:

• Port can modify MAC address table with any traffic it receives.
• Does not forward traffic except BPDUs.
• 15 seconds

Answer 5

Learning

Question 6

Identify the CST port state:

• Port can forward all network traffic and update MAC address table.
• This is the final port state.

Answer 6

Forwarding

Question 7

Identify the CST port state:

• A configuration or an operational problem on a port that can have major effects has been detected.
• The port discards packets as long as the problem continues to exist.

Answer 7

Broken

Question 8

By default, how long does 802.1D take for a port to transition through all the port states?

Answer 8

30 seconds

Question 9

List the 802.1D port types

Answer 9

Root port
Designated port
Blocking port

Question 10

Original STP from IEEE.

Ensures loop-free topology for one vlan.

Answer 10

802.1D

Question 11

Root of the spanning-tree from which all path calculations are directed towards.

Lowest BID

Answer 11

Root bridge

Question 12

What is a BPDU?

Answer 12

Bridge Protocol Data Unit

Question 13

What destination MAC does a BPDU use?

Answer 13

Multicast 01:80:c2:00:00:00

Question 14

What does the configuration BPDU identify?

Answer 14

Root bridge
Root ports
Designated ports
Blocking ports

Question 15

When is a Topology Change Notifcation (TCN) BPDU sent?

Answer 15

When a link status changes.

Question 16

Combined cost for a specific path toward the root switch.

Answer 16

Root path cost

Question 17

4-bit value that identifies the preference for a switch to be root bridge.

Answer 17

System priority (Bridge priority)

Question 18

What is the default system priority?

Answer 18

32768

Question 19

What is the system ID extension?

Answer 19

12-bit value.

Indicates the VLAN that the BPDU correlates to.

Question 20

What combines to form the root bridge identifier?

Answer 20

Root bridge system MAC
System ID extension
System priority of the root bridge

Question 21

What combine to form the local bridge identifier?

Answer 21

Local switch’s MAC address
System ID extension
System priority of root bridge

Question 22

The maximum length of time that passes before a bridge port saves its BPDU information.

Answer 22

Max age

Question 23

Max age default value

Answer 23

20 seconds

Question 24

What three timers does STP use to make sure that a network converges properly before a bridging loop occurs?

Answer 24

Hello timer
Forward delay
Max age

Question 25

What are the 2 spanning-tree cost modes?

Answer 25

Short mode | Long mode

Question 26

``` STP Port Costs: 10 Mbps 100 Mbps 1 Gbps 10 Gbps ```

Answer 26

``` SM / LM 10 Mbps = 100 / 2,000,000 100 Mbps = 19 / 200,000 1 Gbps = 4 / 20,000 10 Gbps = 2 / 2,000 ```

Question 27

Hello timer default interval

Answer 27

2 seconds

Question 28

Max age default time

Answer 28

20 seconds

Question 29

Forward delay default value

Answer 29

15 seconds

Question 30

What command is used to configure spanning-tree for long-mode interface cost?

Answer 30

spanning-tree pathcost method long

Question 31

What does a BID consist of?

Answer 31

``` Bridge priority (system priority)- 2 bytes MAC address- 6 bytes ```

Question 32

How many bytes make up a BID?

Answer 32

8 bytes

Question 33

Bridge priority range and default value?

Answer 33

Range: 0-65535 Default: 32768 (0x8000)

Question 34

Explain the root bridge election process.

Answer 34

1. Switches send out BPDUs with a root BID equal to its own BID and a sender BID that is it's own BID. 2. Received BPDUs are analyzed to determine if it is a better BPDU. 3. The switch that sent the better BPDU becomes the root bridge. 4. Non-root bridges update their BPDU to advertise the net root BID and root path cost.

Question 35

What determines the root bridge?

Answer 35

1. Lower Bridge priority. | 2. Lower MAC address (if priority is the same).

Question 36

Interface STP cost is used to determine ____ ____ ___ ?

Answer 36

Root path cost

Question 37

Which switch will become the root bridge? Switch A: System priority 16572 MAC 0062.ec9d.c500 Switch B: System Priority 20480 MAC 0062.ec9d.3500 Switch C: System priority 32768 MAC 0062.ec9d.a500

Answer 37

Switch B.

Question 38

What command is used to display the root bridge?

Answer 38

show spanning-tree root

Question 39

Root port election process

Answer 39

1. Interface with lowest path cost. 2. Interface with the lowest system priority of advertising switch. 3. Interface with the lowest MAC address of advertising switch. 4. Lowest port priority, if multiple links involved. 5. Lower port number, if multiple links involved.

Question 40

If two non-root switches are connected on their designate ports, what port state will one of the ports become?

Answer 40

Blocking

Question 41

What determines which port becomes blocked between two non-root switches?

Answer 41

Switch must be a designated port 1. Switch with the higher path cost blocks. 2. Higher system priority blocks. 3. Higher MAC address blocks.

Question 42

List the various STP versions.

Answer 42

``` 802.1D PVST PVST+ 802.1W RSTP 802.1S MST ```

Question 43

What 3 STP modes do Cisco Catalyst switches operate in?

Answer 43

PVST+ RSTP MST

Question 44

What port types are expected on Catalyst switches?

Answer 44

P2P | P2P Edge

Question 45

This type of port specifies portfast is enable on the port.

Answer 45

P2P Edge

Question 46

This port type connects with another network device,

Answer 46

P2P

Question 47

'show spanning-tree' is issued on a switch. The Type field shows *TYPE_INC. What does this signify?

Answer 47

Port configuration mismatch between the switch and the switch it's connected to.

Question 48

True or False: BPDUs always flow from the edge switches to the root bridge in a stable L2 topology.

Answer 48

False. BPDUs originate from the root bridge.

Question 49

True or False: Root bridges contain root ports.

Answer 49

False: All ports on a root bridge are designated ports.

Question 50

What cause a TCN BPDU to be generated?

Answer 50

L2 topology change.

Question 51

What does the root bridge do when a TCN BPDU is received?

Answer 51

1. Creates a new configuration BPDU. 2. Sets the topology change flag. 3. Floods the BPDU to all switches.

Question 52

What does a non-root bridge do when it receives a configuration BPDU with the topology change flag set?

Answer 52

1. Changes MAC address timer to the forwarding delay timer. 2. Flushes all learned MAC address, EXCEPT MACs that are actively communication. 3. Reset MAC address timer to default (300 seconds) when second configuration BPDU is received.

Question 53

True or False: TCNs are generated on a VLAN basis.

Answer 53

True

Question 54

What command shows topology changes?

Answer 54

show spanning-tree [vlan #] detail

Question 55

True or False: A root bridge can generate a configuration BPDU with the Topology Change flag set, without ever receiving a TCN.

Answer 55

True

Question 56

What are the IEEE spanning-tree versions?

Answer 56

802. 1D Common Spanning Tree 802. 1W RSTP 802. 1S MSTP

Question 57

What are the Cisco spanning-tree versions?

Answer 57

PVST PVST+ RPVST+

Question 58

What are the 802.1W port states?

Answer 58

Discarding Learning Forwarding

Question 59

Name the 802.1W root ports.

Answer 59

Root port Designated port Alternate port Backup port

Question 60

Name the 802.1W port types.

Answer 60

Edge port Root port Point-to-point port

Question 61

True or False: 802.1D improve 802.1W by reducing the number of port states a port transitions through to reach the forwarding state.

Answer 61

False 802. 1D is CST. 8021. W is RSTP

Question 62

A port that connects to the root switch or an upstream switch. Has the best path cost toward the root bridge.

Answer 62

Root port

Question 63

A port that provides connectivity to downstream switches and devices.

Answer 63

Designated port

Question 64

A port that provides alternate connectivity toward the root through a different switch.

Answer 64

Alternate port

Question 65

This port only exists when there are multiple links between the same switches. It cannot guarantee connectivity to the root in the event that the upstream switch fails.

Answer 65

Backup port

Question 66

A port where host connect to the L2 topology with one interface and cannot form a loop.

Answer 66

Edge port